1. Field of the Invention
This invention relates to compositions classified in the art of chemistry as dialkyl peroxydicarbonates, more specifically to new and novel thermally-stabilized initiator compositions comprising dialkyl peroxydicarbonates stabilized by the addition thereto of a stabilizing effective amount of at least one stabilizing compound having an ethylenically unsaturated functional group conjugated with an acetylenic or nitrile functional group. The invention further relates to the use of such novel compositions as initiators of polymerization or cure of ethylenically unsaturated monomers, oligomers and polymers. The invention still further relates to the stabilization of dialkyl peroxydicarbonates during their manufacture by the inclusion of a stabilizing effective amount of at least one stabilizing compound having ethylenic unsaturation conjugated with acetylenic or nitrile unsaturation in the mixture of reactants from which a dialkyl peroxydicarbonate is to be prepared prior to, at the commencement of or during the preparative reaction.
2. Description of the Prior Art
Generally, dialkyl peroxydicarbonates which are in liquid form (molten or in solution) above ca. 10.degree. C. are very hazardous owing to auto-accelerated decomposition attributed to induced decomposition of the dialkyl peroxydicarbonate. Strain, et al. (J. Am. Chem. Soc., 1950, 72, 1254-1263) found that auto-accelerated decomposition of diisopropyl peroxydicarbonate (IPP) at room temperature could ##STR2## be largely suppressed by incorporating small quantities of additives such as iodine (1%) phenol (1%), hydroquinone (1%), resorcinol (1%), pyrogallol (1%), tetralin (1%), ethyl acetoacetate (1%), acetanilide (1%), trinitrobenzene (1%), 30% hydrogen peroxide (1%) and several other additives. However, when such stabilizing compositions are used to polymerize vinyl chloride monomer (VCM), there is potential for contamination of the resulting PVC resin by the additives. This contamination is undesirable, both for the PVC resin as well as for the environment. Because the thermally stabilized dialkyl peroxydicarbonate compositions of the instant invention contain only small quantities of free-radically polymerizable unsaturated nitriles or unsaturated acetylenic compounds (such as methacrylonitrile), the stabilizing additives are copolymerized with VCM at very low levels (ca. 1-5 parts per million), and thus do not contaminate the PVC resin or the effluent from the polymerization process.
U.S. Pat. No. 5,155,192 discloses stabilized peroxydicarbonate compositions containing small amounts (0.03 to 3.0 equivalent percent) of compounds containing hydroperoxy groups. Such compositions are claimed to reduce sensitivity to auto-accelerative decompositions, increase safe storage temperatures and increase self-accelerating decomposition temperatures (SADTs). However, polymer producers such as PVC producers do not like to employ initiators containing significant levels of hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide since these impurities are free-radical chain-transfer agents and can become incorporated into the resin molecular chains as peroxy end groups. Such labile end groups can adversely affect the thermal and color stability of the resin. In addition, the lower molecular weight t-alkyl hydroperoxides such as t-butyl and t-amyl hydroperoxides are sufficiently volatile to cause problems during recycle of vinyl chloride and other monomers.
The thermally stabilized dialkyl peroxydicarbonate compositions of the instant invention, which contain compounds having ethylenically unsaturated groups conjugated with nitriles or ethylenically unsaturated groups conjugated with acetylenic groups advance the peroxide art and the polymerization art since they do not cause the above resin stability problems or monomer recycle problems.
It is generally known to organic peroxide producers, see the Strain reference cited above, that lower molecular weight dialkyl peroxydicarbonates (such as diisopropyl peroxydicarbonate), which are in the liquid state during their production by reaction of an alkyl chloroformate with an aqueous solution of hydrogen peroxide and an inorganic base such as sodium hydroxide or potassium hydroxide, can be thermally stabilized and prevented from undergoing auto- or self-accelerating decomposition during manufacture by bubbling oxygen gas or an oxygen containing gas, e.g., air, through the reaction mixture. However, in such processes at least one settling of the reaction mixture into an upper organic phase (dialkyl peroxydicarbonate) and a lower aqueous phase is required. During these separations, agitation necessarily is terminated and bubbling of oxygen gas or an oxygen containing gas is stopped in order to enable complete separation of phases. During this quiescent period the organic dialkyl peroxydicarbonate phase is deprived of oxygen stabilizer and a hazardous self-accelerating decomposition of the liquid dialkyl peroxydicarbonate phase can occur.
This invention provides a novel manufacturing process of enhanced safety for production of liquid dialkyl peroxydicarbonates. The process employs a small quantity of an ethylenically unsaturated nitrile or acetylenic compound during processing for enhancing the thermal stability of the liquid dialkyl peroxydicarbonate during manufacture, thus suppressing self-accelerating decomposition of the liquid peroxydicarbonate during manufacture and enhancing the thermal stability of the liquid dialkyl peroxydicarbonate during subsequent storage and handling.
The novel processes providing enhanced safety for the manufacture, storage, handling and use of pure liquid dialkyl peroxydicarbonates can be of the batch type, continuous type or semi-continuous type.
It should be noted that the addition of the organic hydroperoxide stabilizers for dialkyl peroxydicarbonates known in the art, such as those provided by the aforementioned U.S. Pat. No. 5,155,192, during the process for production of pure liquid dialkyl peroxydicarbonates would not be effective for thermally stabilizing the dialkyl peroxydicarbonates during processing or subsequent to processing since the art organic hydroperoxide stabilizers are reactive with alkyl chloroformates, forming OO-t-alkyl O-alkyl monoperoxycarbonates: ##STR3## which are not known stabilizers for dialkyl peroxydicarbonates. Furthermore, many of the organic hydroperoxides of the art are likely to partition into the aqueous phases that are involved in dialkyl peroxydicarbonate manufacturing processes, and, thus, the thermal stabilizers would not be present in the organic dialkyl peroxydicarbonate phase where thermal stabilization is needed. Therefore, the stabilizing compounds having an ethylenic unsaturated functional group conjugated with an acetylenic or nitrile functional group, especially the unsaturated nitriles or the unsaturated acetylenic compounds of Structure I of this invention are also superior to the stabilizers previously known for thermally stabilizing dialkyl peroxydicarbonates during production.